1. Field of the Invention
The present invention relates to a magnetic base adapted to be used, for example, for supporting a measuring instrument such as a strain gauge by a post and/or arm provided on the magnetic base which in turn is secured by a magnetic force to a magnetic substance and more particularly to a magnetic base which is switchable to be engaged or released from such a substance by an operation of rotating a permanent magnet disposed rotatably in a magnetic circuit block.
2. Description of the Prior Art
In the conventional magnetic base of this type known heretofore, the magnetic active surface of a magnetic circuit block may be placed into an excited state or an unexcited state by rotating a permanent magnet housed rotatably in a cavity formed in the block.
For the permanent magnet incorporated in such a magnetic base, it has been customary to use an alnico magnet having a large residual magnetic flux density. However, in the conventional base equipped with an alnico magnet, a great rotatory resistance resulting from a magnetic force is exerted at a given angle during the rotation of the magnet from an unexcited state to an excited state, hence causing difficulty in achieving a light and smooth switching operation.